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Cabbage Loopers: All About Trichoplusia Ni And How To Eliminate Them

There’s something crawling along the leaves of your arugula, and it looks like a little inchworm. It’s green, and it is snacking as it goes, leaving holes throughout your plants. There’s another on your cabbage, and another one on your radish leaves. What’s going on here?

You have just discovered the cabbage looper in your garden, and if you don’t hurry, they will eat it before you ever have the chance to taste it yourself. So today, I’m going to tell you how to eradicate this moth and its inchworm-like offspring from your yard, and hopefully you will be able to rescue your plants!

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Cabbage Looper Overview

Common Name(s) Cabbage looper, Cabbage moth, Ni moth
Scientific Name(s) Trichoplusia ni
Family Noctuidae
Origin North America, Africa, Europe, Asia, Australia
Plants Affected Prefer plants with natural glucosinolates/glucosides. These plants include cabbage, kale, broccoli, cauliflower, collards, turnips, radishes, mustard greens, and many more. Also can impact beets, melons, some beans, celery, cucumbers, parsnips, peas, peppers, potatoes, spinach, squash, lettuce, thyme, tomatoes, and other vegetable crops.
Common Remedies Handpicking eggs from plants, spraying with Bacillus thuringiensis var. Kurstaki (BT) or natural oil sprays such as garlic oil, introducing or encouraging their natural predators, spreading diatomaceous earth, using cabbage netting to prevent egg-laying.

Types of Cabbage Loopers

There are other moth or butterfly insects from the Lepidoptera order which are commonly confused with cabbage loopers. These include the cabbage worm (Pieris rapae or Pieris brassicae spp.), the cabbage moth (Mamestra brassicae), the cabbage webworm (Hellula undalis), the orange tip butterfly (Anthocharis cardamines), and the diamondback moth (Plutella xylostella or Plutella maculipennis). Their life cycles and reproduction may be different from the cabbage looper, but they tend to attack similar plants, and often can be eliminated in similar ways.

But for this particular piece, we’re going to focus on the actual cabbage looper, Trichoplusia ni.

Trichoplusia ni, ‘Cabbage Looper’, ‘Cabbage Moth’, ‘Ni Moth’

The cabbage looper (Trichoplusia ni) in its caterpillar and moth state.
The cabbage looper (Trichoplusia ni) in its caterpillar and moth state. Source: ajmatthehiddenhouse for moth and Jaume Torán for the caterpillar.

The term “looper” derives from the way the looper caterpillar crawls. Much like an inchworm, it hunches itself up in an arched or looped shape and then propels itself forward. Its scientific name and the term “Ni moth” both come from a pattern common on the wing of the adult brown moth, which resembles the lowercase Greek letter ‘ni’. The reference to cabbage originates with the caterpillar’s fondness for brassicaceae plants.

It is a voracious feeder in its larval or caterpillar state, and primarily consumes leaf greens rather than stems or veins. It can bore into some vegetables like cabbage or cauliflower, leaving waste behind that renders the plant inedible for humans. And it can quickly devour your vegetable garden.

Life Cycle of Cabbage Loopers

Life cycle of the cabbage looper
Life cycle of the cabbage looper. Source

An adult cabbage looper moth lays multiple pale yellow, round eggs on each plant, both on the tops and bottoms of the leaves chosen. Each female can lay between 300-600 eggs in the 10-12 day adult lifespan. These eggs will hatch in 3-10 days.

The emerging caterpillars are pale white, but gradually turn green with yellowish stripes along their back. They also start out looking somewhat hairy, but gradually lose these hairy spines as they mature. Over the 3-4 week larval stage, they grow and mature, going through color shifts and moulting stages, and it is during this larval stage that they consume vast amounts of leafy matter.

They then form a pupa or cocoon, and somewhere between 4-12 days later they will emerge as full-grown adult, semi-nocturnal moths. In warmer temperatures, the pupal stage is much more rapid. They are considered semi-nocturnal because they will sometimes emerge at or just before dusk to mate and feed, but they are far more active during the nighttime hours.

Common Habitats for Cabbage Loopers

Like cabbage worms, cabbage loopers live where their food is, and that means that they can turn up nearly anywhere where food for humans is grown. However, while their diet is incredibly wide, they tend to prefer brassica-species plants to lay their eggs on due to the high glucosinolate content. They lay their eggs on both the top and bottom of the leaves of their chosen host plant.

What Do Cabbage Loopers Eat?

Cabbage loopers prefer plants which produce natural glucosinolates or glucosides, and that includes nearly every cruciferous food plant. While I provided a short list in the overview, here’s a more extensive list of edible cruciferous plants which cabbage loopers prefer, both for egg-laying and for feeding purposes:

  • Cabbage
  • Turnips
  • Broccoli
  • Cauliflower
  • Bok choy
  • Kale
  • Napa cabbage
  • Garden cress
  • Brussels sprouts
  • Collard greens
  • Horseradish
  • Savoy cabbage
  • Watercress,
  • Broccoli romanesco
  • Mizuna
  • Bomdong
  • Kohlrabi
  • Broccoli rabe
  • Choy sum
  • Cime di rapa
  • Gai lan (Chinese broccoli)
  • Komatsuna
  • Arugula
  • Radish
  • Daikon
  • Wasabi
  • Tatsoi
  • Mustard greens (white, Indian, Ethiopian and black mustards)
  • Rutabaga

Cruciferous vegetables are not the only targets of cabbage looper caterpillars. They are also quite willing to munch on beets, cantaloupe, celery, cucumbers, lima beans, lettuce, parsnips, peanuts, peas, peppers, potatoes, snap beans, spinach, soybeans, squash, sweet potatoes, thyme, tomatoes, and watermelon.

As you can see, these little inchworms are destructive… very, very destructive. And they are not picky eaters, so you have to destroy them as quickly as you find them.

How To Get Rid Of Cabbage Loopers

Figuring out how to get rid of cabbage worms and cabbage loopers is surprisingly similar, as is eliminating many other forms of caterpillar. Let’s look at some of the most common options to figure out what you should do.

Organic Cabbage Looper Control

The first step in cabbage looper control is to try to eliminate eggs when you find them. As they are common on both the top and bottom of the leaves, it can be easier to discover a problem with loopers than with other cabbage worms. Hand-pick the eggs off the leaves while wearing gloves, and drown the eggs in soapy water or crush them to prevent hatching.

Bacillus thuringiensis var. kurstaki is the most popular method to get rid of cabbage loopers

By far, the most popular way to eliminate cabbage loopers is by using Bacillus thuringiensis var. kurstaki (also referred to as BT or BTK), a bacteria which creates poison in the looper’s gut after it’s consumed. This is available as both a foliar spray or as a fine dust, and both work quite well to eliminate most caterpillars that prey on produce, including looper caterpillars. However, it should be noted that in some very limited conditions (primarily greenhouse conditions, where only the strongest of the species tends to survive), there have been cases of loopers who appear to be BT-resistant. This has not shown up in outdoor conditions, and it is a fairly uncommon occurrence.

Spinosad spray for cabbage loopers

Organic insecticides such as spinosad or pyrethrin are also quite effective against any of the caterpillar species, but they must be handled with caution. These present a very small danger if inhaled during spraying, and you should work with gloves on to keep these insecticides off your skin.

Diatomaceous earth is a good cabbage looper preventer

Diatomaceous earth powder is another popular method to control the spread of caterpillars and other insects. Made of crushed shell, the food-grade diatomaceous earth can be spread on all parts of the plant. It is not harmful to humans or larger animals like pets, but to insects, it’s like glass… it cuts their soft skin and causes them to dehydrate and die.

Environmental Cabbage Looper Control

Trichogramma wasps are an environmental cabbage looper control method

Using parasitic insects such as Trichogramma wasps to eliminate cabbage loopers has proved to be incredibly effective. There are some parasitic flies that also work quite well. Many varieties of birds, both wild and domesticated, will eat cabbage loopers. Among them are house sparrows, skylarks, and domesticated fowl such as chickens, turkeys, and ducks.

Preventing Cabbage Loopers

When looking at how to get rid of caterpillars naturally, one of the best ways that I’ve discovered is to keep them from reaching the plants at all. If you use a floating row cover of fine nylon mesh over your plants, it prevents the cabbage looper moth from laying their eggs on it entirely.

Another option is to use a garlic spray that discourages the butterflies from laying eggs on your plants. You can buy garlic oil sprays, but you can also make your own.  This works for June bugs, squash bugs, cabbage worms and cabbage loopers, aphids, and a variety of other insects. Adding a little mint or neem oil to this can be beneficial, too.

Caterpillars also don’t like citrus, so you can make a citrus repellent. Grind up the rinds and seeds of any type of citrus fruit. Soak the ground citrus parts in 2 cups of water overnight, then strain out the pulp. Add 2 teaspoons of dish soap to this and mix thoroughly. Spray all of the plant’s surfaces with that.

Finally, something like neem oil may be a good choice. Neem oil helps to smother the eggs when sprayed onto them, preventing them from hatching. It also acts like a growth retardant, and while it does not completely repel cabbage loopers, it does make the leaves taste bitter to them, which slows the rate at which they consume the plants.

Frequently Asked Questions

Q: Do cabbage loopers eat anything other than edible plants?

A: Unfortunately, yes. These voracious little critters also happily munch on chrysanthemums, hollyhocks, snapdragons, sweetpeas, other brassicaceae family members like alyssum or lunaria, and commercial crops like cotton and tobacco. While it’s less of a concern for them to snack on inedibles, they can still wreak havoc on your ornamentals if they’re left alone. They can also spread from these plants to your edible garden, so keep a watchful eye out for them.

Q: I’ve read that you can salt cabbage loopers to kill them. Does this work?

A: While you can use salt to dehydrate cabbage loopers and slowly kill them, it’s just not as effective as solutions like BT or diatomaceous earth. To be honest, diatomaceous earth is done in a very similar fashion, but as it’s microparticles that act like little knives to the super-soft skin of cabbage loopers (all while not hurting us or our pets at all), it actually is far more effective. Salt also has potential negative impacts on your garden, especially if it builds up over time in your beds. So I don’t recommend using salt in lieu of one of the other options mentioned above.

When you have cabbage loopers, a pinch of prevention is truly worth a pound of cure… or at least a pound of cabbage. So I hope I’ve helped you find the right solution to eradicate these voracious little moth larvae from your prized produce. Have you ever had the war against cabbage loopers before, and did you reign supreme? Let me know in the comments!

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